Considerable research has been directed toward the application of photoalignment layers to various liquid crystal displays because of their advantages, including no extremely small scratches due to rubbing, no mechanical contact and thus no dust and little risk of damage to TFTs, easy patterning, and high resolution. In particular, there is a strong demand for photoalignment layers for horizontal alignment (planar alignment) in IPS/FFS displays. However, photoalignment layers for IPS/FFS have a problem in that image-sticking known as AC image-sticking occurs in display devices unless the photoalignment layers have sufficient anchoring force. AC image-sticking is a defect mode in which a liquid crystal does not completely return to the orientation defined during the manufacture of photoalignment layers when no voltage is applied to the liquid crystal after continued application of voltage. This defect mode also involves a serious decrease in contrast. Accordingly, there is a strong need for a solution to this problem.
As one solution to this problem, there is disclosed a photoalignment layer with an absorption anisotropy parameter defined by taking into account the relationship between the anchoring force and the anisotropy of the alignment layer (PTL 1). This absorption anisotropy parameter is useful for the screening of photoalignment layers for reduced AC image-sticking and is also useful for process condition management during the manufacture of photoalignment layers. However, there are cases where this method cannot sufficiently reduce AC image-sticking.